Honda Stepwagon RK5

It's difficult to find out some information on the Stepwagon RK5 so I thought I'd document my findings here for future reference and to help others.

Back

Head unit

Gathers VXM-135VFNI

Mine came with a Gathers (Panasonic) VXM-135VFNI. It's pretty decent if you're in 2012 still, can read Japanese and live in Japan. The cons of keeping it are:

It's in Japanese. I don't think you can change it. I wouldn't call the UI intuitive but you can learn it with Google translate on a phone in camera mode.
Sat nav only works in Japan
FM radio frequencies differ so you'll only get the bottom end of our frequency range. Converters can be had to adapt the frequency range.
No Bluetooth music (as far as I can tell). It does have Bluetooth but perhaps for calls only.
The touch screen on mine is quite temperamental.

It can be useable though:

It has a CD player. It can even recognise some CDs and display track titles via a built-in Gracenote database. It can even rip them and save them to an SD card for playback via "Music Rack".
SD card slot allows playback of MP3s. It does not support SDXC cards, only SD and SDHC (up to 32GB). It can even display album art if embedded and not a high resolution.

Replacement

Fascia/fitting

It's 2-DIN so you can pop another aftermarket one in there. There's some plug and play Android units that can be had from eBay and Aliexpress. There are also replacement fascias on Aliexpress designed to fit some of the android units with larger screens if yours is broken. This is much cheaper that trying to source OEM but they may not fit all aftermarket units.

Wiring harness

There are also some ISO adapters from InCarTec. If there's steering wheel controls, you'll need a canbus adapter. InCarTec instructions also refer to a Bluetooth module and required wiring but mine didn't have this and works without. I suspect this would be for models with call buttons on the steering wheel (if they exist). It's probably cheapest to replace the existing rear camera too rather than trying to adapt the existing one. The existing wiring can be used but on mine, some of the colours at either end didn't match so check with a DMM. You're also probably best off adding a stick-on windscreen antenna for DAB and removing the existing ones.

Removal of the old

The trim around the radio is likely to be very brittle. I'd say it's impossible to get off without cracking it somewhere.

With a plastic pry tool, pop out the panel directly underneath the screen. This exposes 3 screws.
Undo the left and right crosshead screws (no need to undo the one in the middle).
Adjust the steering wheel down to the lowest level and move the left wiper stalk to the lowest option so that it's easier to get the trim past it.
Stick a nice thick cloth below it and over the gear selector so that you're less likely to damage stuff.
There are push clips along the top and bottom. Pull it off from the bottom and around the top and vents carefully.
You can now remove the connectors from the back of the unit. The main connector has a lever to release it. You probably will need to pry it open with a tool as it may be fairly stiff.

Pin outs / wiring

I haven't figured out every wire but this should help a lot.

Rear of OEM head unit with connectors labelled

Main connector - Power and speaker output
1 - Antenna
2 - Reverse indicator
3 - Not sure, unused. Possibly USB
4 - USB
5 - ETC card reader
6 - Antenna (Either for ETC, DTV, GPS or something else)
7 - Antenna (Either for ETC, DTV, GPS or something else)
8 - Antenna (Either for ETC, DTV, GPS or something else)
9 - Antenna (Either for ETC, DTV, GPS or something else)
10 - Not sure, unused. Looks similar to reverse camera on other Honda head units.
11 - Not sure, unused
12 - Microphone
13 - Reverse camera
14 - Not sure, unsed
15 - FM antenna

Connectors are labeled from left to right, top to bottom, looking from the back where the wires enter from the loom.

Main connector

Pin	Colour	Description
1	-	Unused/unknown
2	-	Unused/unknown
3	-	Unused/unknown
4	-	Unused/unknown
5	Pink	Unknown
6	Brown	Speaker
7	Light green	Speaker
8	-	Unused/unknown
9	-	Unused/unknown
10	Peach	Speaker
11	Blue	Speaker
12	Brown	Ground
13	Light brown	Unknown
14	Red	12v switched
15	Green	Unknown (5v)
16	Light pink	Unknown
17	-	Unused/unknown
18	Dark green	Speaker
19	Red	Speaker
20	-	Unused/unknown
21	-	Unused/unknown
22	Orange	Speaker
23	Light brown	Speaker
24	Blue (silver stripes)	Permanent 12v

Connector 2

Reverse

Pin	Colour	Description
1	-	Unused/unknown
2	Red (with silver stripes)	12v when reverse engaged
3	Peach	Ground

Subwoofer install

Power cable

The easiest place I could find was behind the glovebox between the existing wiring harness and air conditioner in/out. Drilling a hole here may need a 300mm drill bit as there's little space for the drill. Aim for around level with the existing harness (hidden behind the blower) and lower down than the air conditioner pipes. There's a clip in the engine bay holding an air conditioner line that you want to come out below.

Top of transmission showing the fitting removed exposing the end of the filter

Wiring

Removing the passenger side front and rear kick plates expose the Steppy's wiring harness running to the rear and you can run cable to an amp/subwoofer along there.

Amp location

I fitted a small VIBE POWERBOX400.1 amp under the passenger seat bolted to the side. The wiring can come out where the seat attaches to the chassis and be hidden under the trim pieces. I also fitted a Pioneer GM-D1004 which is stuck with double-sided tape right above the glovebox and connects in-line with the ISO harness.

Subwoofer

I went with the Rockford Fosgate R2S-1X12 as this will fit underneath the rear seats and can be positioned in such a way that they can still be folded back down into the floor. The subwoofer remains kind of in the way here but you could move it further forwards to gain boot/trunk space when the rear seats aren't in use.